Two general methods of knurling are known. Knurling is typically performed by the first knurling process, referred to as roll knurling or form knurling. Form knurling is done by pressing a knurling wheel against a workpiece with sufficient force to plastically deform the outer surface of the workpiece. The second knurling process, referred to as cut knurling, is performed by orienting the knurling wheel relative to the workpiece such that the wheel cuts a pattern into the workpiece by removing metal chips. Cutting knurl holders and cutting knurl wheels are available from Dorian Tool International, Houston, Tex. Zeus brand cutting knurl tools are available from Eagle Rock Technologies Int'l Corp. of Bath, Pa.
In form knurling, the rotational axis of the knurl wheel is parallel to the rotational axis of the cylindrical workpiece. Therefore, the helix angle of the grooves formed on the roll is defined by the helix angle of the teeth on the knurl wheel. For cut knurling, the rotational axis of the cutting knurl wheel is tilted with respect to the rotational axis of the cylindrical workpiece ("the tilt angle") to define the helix angle and to produce the cutting action. Because the edge of the knurl wheel is being used as a cutting tool, it is necessary to provide a clearance angle. This is achieved by positioning the knurl wheel so that at the point of contact of the knurl wheel and workpiece surface, the toothed cylindrical surface of the knurl wheel and the workpiece surface form an angle of 3 to 10 degrees.
In both of the above types of knurling processes, the structure generated in the workpiece is a plurality of continuous grooves having a cross-section similar to the shape of the teeth on the knurl wheel. Both conventional knurling processes typically impart a diamond-based pattern which is the result of the intersection of two sets of continuous grooves, the two sets having opposite and equal helix angles (one having a left hand ("LH") helix and one having a right hand ("RH") helix) relative to a cylindrical workpiece. The intersection of the two sets of grooves creates a diamond pattern in the outer surface of the workpiece. The diamonds are aligned in the direction perpendicular to the longitudinal axis of the cylindrical workpiece, and are all substantially identical to one another. Conventional knurling processes have also been used to impart a square-based pattern, in which the squares are oriented to have their sides at 45.degree. to the longitudinal axis of the workpiece. As with the diamond-based pattern, the square-based pattern is also aligned in the direction perpendicular to the longitudinal axis of the cylindrical workpiece, and all of the square-based pyramids are identical. These processes are typically used to impart a non-slip pattern on a tool handle, machine control knob, or the like.
In common commercially available cut knurling holders, the knurl wheel tilt angle is fixed at .+-.30.degree. relative to the rotational axis of the cylindrical workpiece. Holders providing a .+-.45.degree. knurl wheel tilt angles are also available. Knurl wheels with teeth having helix angles relative to the rotational axis of the wheel of 0.degree., 15.degree. RH, 30.degree. RH, 15.degree. LH and 30.degree. LH are readily available. The sum of the tilt angle and the tooth helix angle defines the groove helix angle in the workpiece. The permutations of arithmetic sums of these wheel axis tilt angles and knurl teeth helix angles can produce groove helix angles on the cylindrical workpiece surface at 0.degree., 15.degree., 30.degree., 45.degree., 60.degree. and 75.degree. RH or LH to the workpiece rotational axis. If a groove helix angle on the workpiece surface other than these angles is desired, a special knurl wheel and/or knurl holder must be fabricated.
WIPO International Patent Application Publication Number WO 97/12727, published on Apr. 10, 1997, "Method and Apparatus for Knurling a Workpiece, Method of Molding an Article With Such Workpiece, and Such Molded Article," Hoopman et al., discloses a method and apparatus for knurling a workpiece in which the two sets of intersecting grooves each have a helix angle of unequal magnitude and opposite direction. The resulting knurl pattern is therefore not aligned in the cylindrical direction of the workpiece. Hoopman et al. also discloses a method of molding a molded article with the knurled workpiece to impart the inverse of the knurl pattern onto the molded article, and a method of forming a structured abrasive article with the molded article. The structured abrasive coating comprises abrasive particles and a binder in the form of a precise, three dimensional abrasive composites molded onto the substrate.
Other structured abrasives, and methods and apparatuses for making such structured abrasives, are described in U.S. Pat. No. 5,152,917, "Structured Abrasive Article,"(Pieper et al.), issued Oct. 6, 1992, the entire disclosure of which is incorporated herein by reference.
WIPO International Pat. Application Publication Number WO 95/07797, "Abrasive Article, Method of Manufacture of Same, Method of Using Same for Finishing, And a Production Tool," (Hoopman et al.), published Mar. 23, 1995, discloses a structured abrasive article in which the abrasive composites are not all identical. Hoopman et al. provides differing dimensioned shapes, among other things, in the array of abrasive composites. A copy of a desired pattern of variably dimensioned shapes of abrasive composites can be formed in the surface of a so-called metal master, e.g., aluminum, copper, bronze, or a plastic master such as acrylic plastic, either of which can be nickel-plated after grooving, as by diamond turning grooves to leave upraised portions corresponding to the desired predetermined shapes of the abrasive composites. Then, flexible plastic production tooling can be formed, in general, from the master by a method explained in U.S. Pat. No. 5,152,917 (Pieper et al.).
Other examples of structured abrasives and methods and apparatuses for their manufacture are disclosed in U.S. Pat. No. 5,435,816, "Method of Making an Abrasive Article," (Spurgeon et al.), issued Jul. 25, 1995, the entire disclosure of which is incorporated herein by reference. In one embodiment, Spurgeon et al. teaches a method of making an abrasive article comprising precisely spaced and oriented abrasive composites bonded to a backing sheet. Spurgeon et al. teaches that, in addition to other procedures, a thermoplastic production tool can be made according to the following procedure. A master tool is first provided. The master tool is preferably made from metal, e.g., nickel. The master tool can be fabricated by any conventional technique, such as engraving, hobbing, knurling, electroforming, diamond turning, laser machining, etc. The master tool should have the inverse of the pattern for the production tool on the surface thereof. The thermoplastic material can be embossed with the master tool to form the pattern. While Spurgeon et al. mentions briefly that the master tool can be made by knurling, no specific method of knurling a master tool is shown, taught, or suggested by Spurgeon et al.
Thus it is seen that there is a need for a knurling apparatus and method that allows the knurl wheel to be held at any desired angle relative to the rotational axis of a cylindrical workpiece. There is also a need to provide a knurling apparatus and method in which the knurling pattern in the workpiece comprises groove structures of at least two different configurations.